Glycogen, known as a storage polysaccharide in animals, is a highly-branched polymer in which a large amount of glucose is linked by α-1,4 glycosidic linkages. Glycogen is made primarily in the liver and skeletal muscles and functions as a transient storage medium for excess glucose.
Glycogen synthesis and breakdown is regulated by tyroxine, glucagon, insulin, adrenalin, etc., which are secreted depending on the physiological state, e.g., blood glucose level.
Although glycogen-containing compositions are known (Patent Document 1), almost no studies are conducted on their role other than those of energy storage and immune system activation (Non-Patent Document 1).
Glycogen can be obtained from animals (e.g., oysters) or plants; however, synthesized products are also known and their anticancer effects are studied (Non-Patent Document 1). Patent Document 2 discloses a production process of glycogen.    Patent Document 1:    Japanese Unexamined Patent Publication No. 2000-007707    Patent Document 2:    WO2006/035848    Non-Patent Document 1:    Ryoyama, K.; Kidachi, Y.; Yamaguchi, H.; Kajiura, H.; Takata, H. (2004) Biosci Biotechnol Biochem 68, 2332-2340